A this time, broadcast television operates in accordance with a standard defined by NTSC (National Television Standards Committee). Over the next few years, the NTSC television standard is going to be phased out and replaced with a new standard to which present day HDTV conforms.
The HDTV standard for transmission uses a scheme called 8-VSB modulation as the means to convey MPEG II data (the video and audio information) from the transmitters to the receivers. The MPEG II video compression along with the 8-VSB modulation forms the transport layer for HDTV transmission. The original video information is thus processed prior to transmission, and this requires a considerable amount of processing to provide an acceptable degree of robustness in the system.
The receivers need all (100%) of the transmitted MPEG II data or unacceptable gaps in the audio and video will result. Since significant amounts of the transmitted data may be corrupted during transit from the transmitter to the receivers due to weather, power transients, etc., any lost data must be reconstructed by the receivers without retransmission of the original data by the transmitter. Such reconstruction is provided by the transport layer and requires a large amount of processing at the transmitter to keep pace with the data rate used by the HDTV system. Even though the operating speeds of silicon ICs are extremely fast and are increasing, the hardware presently required to encode the MPEG II data stream in real time is very expensive and not readily available.
Briefly, there is provided in accordance with the present invention a new and improved method of generating an 8-VSB signal which enables the use of software to replace much of the hardware now required to accomplish most of the processing of the MPEG II data before it is transmitted or stored in some suitable storage media. Once the MPEG II data has been stored in its pre-encoded or partially encoded form, a minimum amount of hardware can be used to retrieve the stored information and perform the final stage of 8-VSB modulation, which entails only a small amount of processing.